This invention relates to aqueous high solids slurries comprising aluminum trihydrate and blends of such slurries comprising titanium dioxide slurries for use in paper, coatings and plastic applications, especially for use in indirect food-contact paper.
Aluminum trihydrate (ATH) can be used as a filler to produce coatings for paper and paperboard. Because of the relative high cost of titanium dioxide (TiO2), paper mills often replace or extend titanium dioxide with less expensive pigment alternatives, such as ATH, calcium carbonate, kaolin clays and the like. The extender may reduce or eliminate the need for the more expensive white titanium dioxide pigment.
Typically pigments and fillers are introduced into papermaking processes in the form of aqueous slurries. Commercial slurries of ATH are available, but they typically contain organic chemicals that are not compliant with United States Food and Drug Administration (FDA) regulations 21 C.F.R. 176.170 and 21 C.F.R. 176.180 for use in paper with indirect food contact. Even if a paper product is not intended for indirect use with food, paper manufacturers do not typically separate their lines for food and non-food use.
For a slurry to be useful in paper and paper-board applications, the paper manufacturer must be able to pump the slurry from storage into the paper furnish or into the coating make-up area. Pigment slurries at high percent solids are desired to reduce drying energy and increase production rates through the paper coater dryer. High solids slurries combined with low viscosity also improve the flow through the coater to avoid coating scratches and streaks on the final coated paper surface. In order for an ATH slurry to be considered useable as an extender pigment filler or for blending with TiO2 slurry, the ATH pigment solids content should be greater than 50 wt. % and preferably 67.5 wt. % or higher. At such high solids content the available ATH slurries often have unacceptably high viscosities for either indirect use or use as a slurry to be blended with TiO2 slurries.
U.S. Pat. No. 4,376,655 discloses aqueous titanium dioxide slurries comprising ATH and kaolin clays. The ratio of TiO2 to alumina is between 1000:1 and 2000:1. The ATH useful can either be a 9-10% aqueous slurry or a 50-55% dried gel. Preferably the dried gel contains occluded carbonates.
U.S. Pat. No. 5,015,334 discloses a dispersable colloidal silica material, which is a clay, including Laponite® brand synthetic hectorite clays, associated with an anionic organic polymer for use as a retention agent in papermaking.
U.S. Pat. No. 5,171,631 discloses a titanium dioxide pigment ATH extender/spacer pigment composition comprising 70-98% titanium dioxide by volume and 2-30% ATH by volume wherein the ATH has a similar median particles size as the titanium dioxide. Typically the median particle size of the titanium dioxide is 0.2 to 0.3 microns. The ATH has a median particle size within ±20% compared to the titanium dioxide particle size. An example of a coating composition comprising the pigments was prepared with titanium dioxide and ATH and contained a cellulosic thickener, associative thickener, propylene glycol, nonionic surfactant, neutralizer defoamer, coalescing agent and biocide, in water at a solids content of 3.23%.
U.S. Pat. No. 5,342,485 discloses use of ATH with improved whiteness in papermaking to reduce costs relative to using solely TiO2. This patent discusses use of ATH in slurries at 15-30% solids.
U.S. Pat. No. 5,571,379 discloses a composition comprising hectorite clay, acrylic polymer and other additives commonly used in the manufacture of paper or paperboard, including fillers and pigments such as TiO2. There is no disclosure of use with ATH or of hectorite clay reducing the viscosity of an aqueous slurry of TiO2 or ATH.
U.S. Pat. No. 5,676,748 discloses an aqueous slurry for use as providing filler for paper and paperboard products comprising 1 to 30 wt. % solids of mineral particles with a distribution of coarse (>0.5 microns) and fine particles (<0.2 microns) and an anionic acrylic dispersing agent and a cationic flocculating agent. However, slurry of the minerals may be up to 70-76% solids that must be diluted for use, for example, at a paper mill. Examples are limited to kaolin clays.
U.S. Pat. No. 5,824,145 discloses a photodurable titanium dioxide slurry which comprises at least 78% titanium dioxide particles and at least 3% alumina particles along with a dispersant, which can include polyacrylates, alcoholamines, citric acid, and the like with a pH of about 6.0 to 9.0.
U.S. Pat. No. 6,387,500 discloses coating formulations for paper and paperboards comprising aqueous slurries of titanium dioxide pigment with extender pigments, which include ATH and calcined clay, and dispersants, which include acrylates. There is no mention of combining with synthetic hectorite clay to improve viscosity and rheology.
Therefore, there remains a need to decrease the cost of opacity in paper and paper-board applications. There is a need to provide an ATH slurry with improved viscosity and rheological properties. There is a need to find suitable ATH slurry compositions that are of suitable viscosities for use in paper applications including FDA compliant and non-FDA compliant compositions. There is also a need for ATH slurry compositions compatible with titanium dioxide slurries that are stable at suitable viscosities and are FDA compliant for indirect food contact. The present invention meets these needs.